Ok, here it is: I was driving down the road today with the wife. We have the stereo and the air going and all is well. Suddenly I heard this weird constant clicking noise at a rapid rate, similar to the pace of a kid riding a bike with playing cards in the spokes but much quieter. I turned off the radio and the air, but the noise continues. I was able to track the noise down to the small vent-looking thing above the driver's door. It is the only one visible in the cab. Anyway, when I got home and shut the truck off, the noise stopped, but slowly, like the bike was slowly decelerating before coming to a complete stop. Then I turned the key forward but stopped before starting the engine, and the noise slowly wound it's way back up to its previous pace. What the hell is the vent, the cause of the noise, and the fix?

 

It sounds like a small fan of some sort... sounds really similar to something my cpu fan is doing in my computer

just a thought

 

I agree, that's why I killed the HVAC; why the hell would there be a stupid little fan there?